MELBOURNE, Australia — Novak Djokovic recalled his own brush with match-fixing, as the start of the year’s first Grand Slam tournament was overshadowed by corruption allegations.

Djokovic started his bid for a sixth Australian Open title with a 6-3, 6-2, 6-4 win over Chung Hyeon of South Korea on Monday, hours after the BBC and Buzzfeed News published reports alleging match-fixing had gone unchecked in tennis.

No players were identified in the reports, which alleged 16 players had been flagged repeatedly with tennis authorities but not sanctioned on suspicion of match fixing. Half of those are entered in the Australian Open, the reports said.

The governing bodies for the sport, and the Tennis Integrity Unit, issued a joint statement, read by ATP chairman Chris Kermode at a hastily-convened news conference at Melbourne Park.

Kermode said tennis authorities “absolutely reject any suggestion that evidence of match-fixing has been suppressed for any reason, or isn’t being investigated.”

Djokovic later responded to a question about an approach ahead of a tournament in St. Petersburg, Russia, in 2007.

“I was approached through people that were working with me at that time, that were with my team,” he said. “Of course, we threw it (the approach) away right away. It didn’t even get to me. The guy that was trying to talk to me, he didn’t even get to me directly. There was nothing out of it.

“Unfortunately there were some, in those times, those days, rumors, some talks, some people were going around. They were dealt with. In the last six, seven years, I haven’t heard anything similar.”

Djokovic was an up-and-coming player at the time, not winning the first his 10 major titles until the 2008 Australian Open.

“It made me feel terrible because I don’t want to be anyhow linked to this kind of – you know, somebody may call it an opportunity,” he said. “For me, that’s an act of unsportsmanship, a crime in sport honestly. I think there is no room for it in any sport, especially in tennis.”

Djokovic said he thought the allegations related to matches from almost 10 years ago and didn’t involve active players.

Roger Federer, a 17-time major winner and former leader of the player council, agreed the allegations likely weren’t new but remained “super serious.”

“I would love to hear names,” Federer said. “Then at least it’s concrete stuff and you can actually debate about it. Was it the player? Was it the support team? Who was it? Was it before? Was it a doubles player, a singles player? Which slam?

“It’s super serious and it’s super important to maintain the integrity of our sport. So how high up does it go? The higher it goes, the more surprised I would be, no doubt about it.”

Serena Williams was on court preparing for her opening 6-4, 7-5 win over No. 34-ranked Camila Giorgi when Kermode was holding a news conference to respond to the fixing allegations.

Like Djokovic, Williams won three of the four major titles last season, but hadn’t finished a competitive match for months. She withdrew from the Hopman Cup because of inflammation in her knee, playing just one set in Perth.

“I haven’t played in a long time, but I have been playing for 30 years, so it’s kind of – I try to focus on that,” Williams said. “I was able to stay in it and stay calm today and I think that’s what matters most.”

The 21-time major winner said there was no hint of match-fixing on the women’s tour.

“I play very hard, and every player I play seems to play hard,” she said. “As an athlete, I do everything I can to be not only great, but, you know, historic.”

Maria Sharapova, who lost to Williams in the final here last year and could meet her again in the quarterfinals, showed no signs of a left forearm injury that curtailed her preparations when she beat Nao Hibino 6-1, 6-3 in a night match. Genie Bouchard advanced with a 6-3, 6-4 win against Alexandra Krunic.

Former No.1-ranked Caroline Wozniacki lost 1-6, 7-6 (3), 6-4 to Yulia Putintseva, continuing a downward spiral at Melbourne Park that has resulted in her exiting one round earlier each year since she reached the 2011 semifinals.

The former top-ranked player and owner of five major titles, including the 2006 U.S. Open, tested positive for the newly banned drug meldonium at the Australian Open in January 2016. That led to a 15-month doping ban, which expired in April.

“Such a special, special tournament, and victory for me, one that I’ll remember forever,” Sharapova said. “Sometimes you never know when it will all come together but it happened to me this week in Tianjin.”

Sharapova displayed resilience as she came from behind in both sets to overcome her 19-year-old opponent.

Sabalenka led 4-1 in the opener and 5-1 in the second before relenting to Sharapova’s greater big-match experience. It was Sharapova’s 36th WTA singles title.

The 30-year-old Sharapova played in her first Grand Slam tournament following the ban at the U.S. Open in August, where she reached the fourth round. Sunday’s result will lift Sharapova up to No. 57 in the world rankings.

SHANGHAI (AP) Roger Federer extended his winning streak over Rafael Nadal this year to four matches after beating the top-ranked Spaniard 6-4, 6-3 to win the Shanghai Masters on Sunday.

The Swiss 19-time grand slam winner, who still trails Nadal 23-15 in their overall head-to-head record, didn’t face a break point and started and ended the match with service breaks.

“I don’t know what my expectations were going in,” Federer said. “I thought I might struggle early on because it was a late finish last night.

“I had no nerves before the match, surprisingly. I think I was pretty clear about how I wanted to play the match. I started off very well and relaxed from then on.”

Despite his dominance in 2017, Federer doesn’t rate his chances of catching Nadal in their head-to-head record.

“It’s not going to happen. We don’t have enough years left on the tour. We ranked too good so we play each other only in finals at the moment… You can’t win them all against Rafa, to be honest. He’s too good of a player,” Federer said.

Federer took advantage of three of seven break point opportunities in the match to snap Nadal’s 16-game winning streak, which included his China Open victory last week.

Federer, who has won the last five encounters between the pair dating back to the 2015 Basel final, also beat Nadal in the Australian Open final, a round of 16 match at Indian Wells and the Miami final this year.

“Have been a very difficult match for me,” Nadal said. “He played very fast and he played well.

“Of course was not the best match for me of the week. When somebody plays better than you, sport is not very difficult. That’s the real thing, no? When you play against somebody that is better than you in most of the things that really matters in this sport, in this kind of surface, then it’s tougher.”

The Shanghai Masters is Federer’s 94th career title, moving him into a tie with Ivan Lendl in second place on the Open era list.

Nadal arrived on court with a bandage under his right knee, the same leg he twice smacked with his racket after losing his serve for the first time this week in the semifinal.

Federer said he was surprised to see the wrap and didn’t feel Nadal was struggling with his movement.

In his post-match press conference, Nadal elected not to discuss the knee injury, saying, “I don’t want to talk about that now, sorry, but after losing final is not the moment.”

When asked if he would play upcoming tournaments in Basel, Switzerland and Paris, Nadal refused to confirm his participation.

Federer took advantage of a third break point in the first game of the match with a winning backhand passing shot. He broke Nadal’s serve again on a second break point in the fifth game of the second set when Nadal sailed a backhand crosscourt wide. In the final game, Nadal netted a forehand at 15-40 to end the 72-minute match.